Ahlberg thought the fact that the group changed the program months after Snowden’s revelations provided good circumstantial evidence that the former contractor had had an impact — but he wanted to see how much.

As it turns out, Recorded Future and Reversing Labs discovered that al-Qaida didn’t just tinker at the edges of its seven-year-old encryption software; it overhauled it. The new programs no longer use much of what’s known as “homebrew,” or homemade algorithms. Instead, al-Qaida has started incorporating more sophisticated open-source code to help disguise its communications.

“This is as close to proof that you can get that these have changed and improved their communications structure post the Snowden leaks,” Ahlberg said.

Others are less sure that you can draw a straight line from Snowden to the changes in al-Qaida’s encryption program. Bruce Schneier, a technologist and fellow at the Berkman Center at Harvard, said it’s hard to tell.